Quantification et impact des défauts sur la structure et les performances de fibres de lin textile en environnements contrastés

Flax, cultivated since ancient times for its fibres, yarns and fabrics, is now emerging as an essential ecological alternative for the textile and composite industries of the future. With its mechanical properties, versatility, traceability and energy efficiency, it represents a material full of potential for innovation and sustainability. However, a number of challenges still limit its optimal exploitation. In six chapters, this thesis explores the impact of flax defects on the structure and performance of its fibres. One of the main challenges in flax scutching is the separation of fibres and co-products, known as shives. Throughout this thesis, new analytical approaches were developed and validated on industrial samples to facilitate the quantification of these shives. At a finer scale, the research focuses on defects in individual fibres, the kink-bands. A multi-scale analysis is carried out to assess the impact of these zones on the mechanical properties of the fibres, taking into account the effects of scutching and hackling conditions. This is followed by a detailed analysis of the local mechanical and biochemical properties of areas with and without kink-bands. In addition, samples of archaeological flax were examined using synchrotron microtomography to study the degradation of flax fibres over time. Finally, hygroscopic tests are performed to observe the behaviour of kink-bands under varying humidity conditions. The results of this latest work open up new perspectives on the potential impact of kink-bands on the wrinkling of flax fabrics.